This invention relates to automotive windshield wiper systems and more particularly to wiper systems which move the wiper to a parking position, preferably located outside the normal wiping area when the system is switched off.
Prior art German specification DE-OS No. 9 17 324 discloses a circuit for a wiper system in which, during normal wiper operation, the wiper moves between two reversing positions, but when the wiper system is switched off, the wiper enters a "depressed" parking position. In this known circuit arrangement the direction of rotation of an electric motor driving the wiper is changed using a reversing switch each time the wiper reaches one of the reversing positions at the borders of the wiping area. By selecting a different switching point of the reversing switch when the operating switch is turned off, the wiper can be directed to a depressed parking position and the electric motor can thereafter be switched off.
In a first embodiment shown in the prior-art specification, three position switches are assigned to the electric motor and are actuated in the depressed parking position as well as in the two reversing positions. The signals from these position switches are evaluated in a switching stage and are used to control a reversing relay. In a second embodiment disclosed in the prior-art specification, the position switches are replaced by a rotational-speed-sensor and the pulses from this rotational-speed-sensor are evaluated by counters and reference stages.
Such wiper systems in which the wipers enter a depressed parking position located in a gap between the engine compartment hood and the windshield have advantages with respect to styling, aerodynamics and especially to safety because during normal operation of the motor vehicle the windshield wipers are out of the driver's sight in a position which in case of an accident cannot injure any persons involved. Safety is also heightened because in this depressed parking position tension on the windshield wiper and consequently the wiper blade can released so that deformations of the blade in the parking position is avoided which deformations could disadvantageously influence the clearness of the wiped area.
On the other hand such wiper systems also have the disadvantage that in winter the windshield wipers might become blocked due to ice and snow which might not totally be excluded in the gap between the hood and the windshield. The electric wiper motor will be damaged if the wiper leaves the parking position after being switched on, but shortly afterwards is blocked in a position in which it is connected to voltage even when the operating switch is off.
Therefore the object of the present invention is to increase the safety and reliability of such wiper systems using simple means.
This object is achieved according to the invention by including means so that the parking position of the wiper can be changed in dependence on the temperature.
The present invention is based on the idea that the wiper can usually be prevented from being blocked if, during winter, the wiper is prevented from entering the gap between the hood and the windshield. This can be realized most easily by changing the parking position in dependence on the temperature. Above a certain threshold temperature the wiper enters its depressed parking position as disclosed in the prior art. However, in temperatures below the threshold, the parking position is changed so that the wiper is parked outside the gap. The low-temperature parking position preferably corresponds to one of the reversing positions during normal wiper operation. This reduces costs because the wiper motor already includes switch contacts for generating signals at these positions. However, solutions are also possible in which in winter the wiper is deposited between the usual reversing position during normal operation and the usual depressed parking position in higher temperatures.
In a preferred embodiment according to the invention the circuit for controlling the wiper system can automatically move the wiper back and forth between its winter and summer parking positions according to the current temperature. If the wiper is in the depressed (summer) parking position (e.g. in the gap) and the temperature falls below the temperature threshold, the wiper is moved into its winter parking position (e.g. example, the reversing position). Similarly, if the wiper is parked in its winter parking position outside the gap, it automatically enters the gap when the current temperature reaches values above the threshold.
Further, the circuit for controlling the wiper system could be modified to allow the use of a manually actuable switch to select one of the possible parking positions. This gives the driver the option of parking the wiper in the depressed parking position in the gap even in low temperatures, since if it is cold but dry there is no danger of the system getting frozen.